Compressor motor swap

[darkk]

I bought a 5 hp compressor at a really good price. Unfortunately it's a 5 hp 208 volt 3 phase motor with a magnetic starter. But..! I got a deal on a 7.5 hp 208 volt single phase and it has 3 capacitors on top in a box. I realize just installing a bigger motor is not going to make the compressor 7.5 hp. I just needed the single phase. Both motors are 3450 rpm. The question...is the 7.5 hp motor going to need a magnetic starter, or are those capacitors there so I can just wire it direct?

 

[Norcal]

Your going to require a mag starter and your existing one may not be rated for your new motor. If it is the & the coil is 208V it needs to be replaced with a 240V coil.

 

[Trey T]

The capacitors are there for phase-shift (starting) and other reasons. You want to keep the magnetic starter to control your motor unless you got other plans.

If that motor do not have thermal protection, then use that magnetic starter kit/box and size the thermal strip (or breaker/fuse) properly.

 

[Norcal]

The capacitors are there for phase-shift (starting) and other reasons. You want to keep the magnetic starter to control your motor unless you got other plans.

If that motor do not have thermal protection, then use that magnetic starter kit/box and size the thermal strip (or breaker/fuse) properly.

That starter can only be used if it is rated for the motor in question.

 

[darkk]

So I need a magnetic starter. Not the end of the world, just another $150 I didn’t want to spend. Lol. Thanks...

 

[sberry]

Need a big ole fat wire tor the 7.5 too.

 

[rsanter]

I converted a large table saw that I got as a three phase unit over to single phase.
I used the same mag start buy buying replacement elements to match the load of the new motor
Easy and cheap swap

 

[walta]

Have you considered powering the 5HP motor with a VFD?

My guess is you could sell the 7.5HP motor for more than the cost of a VFD.

http://www.gohz.com/5hp-vfd

Walta

 

[Norcal]

Have you considered powering the 5HP motor with a VFD?

My guess is you could sell the 7.5HP motor for more than the cost of a VFD.

http://www.gohz.com/5hp-vfd

Walta

You would need a 10 HP drive or larger depending on the manufacturer, since they need to be derated 50% or more with a single phase power source.

 

[alfredeneuman]

The wire you'll need to use is at least #8 if it's THHN in conduit, at least #6 is it's NM.

 

[darkk]

The new VFD’s power loss is not that severe anymore. Like only around 3% I was just checking it out last night. But a mag starter is cheaper. So that’s the route I’ll be going.We have a newer style VFD on our Bridgeport that works really well.

 

[slow]

The larger vfd is due the the fact your only powering it with 2/3 of the input power. I ran 10hp drives on my 7
5 hp fans with single phase input.

 

[david1122]

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Get busy living or get busy dying

 

[stonesfan68]

You need to check out the pressure switch and see if that needs to be changed as well. The motor pulley and belt will also need to be changed.

If that is a model 2475 compressor then it can be run at 7.5HP, although I’d leave it turning at the 5HP speed and have extra capacity in the motor.